Ball Bearings and Miniature Bearings: Dynaroll

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LOAD RATING AND BEARING LIFE

As stated previously, most small bearings are used in applications where rotational accuracy and low torque are primary requirement and loads are light. Therefore the operating lifetime of the bearing is relatively long, and, if properly operated, failure is rare. Nevertheless, all bearings have a finite life under use and will eventually fail to perform satisfactorily due to an increase in noise and vibration, loss of running accuracy, deterioration of lubricant, or fatigue flaking of the rolling surfaces. Such failure modes are considered “normal” and can be predicted using standardized techniques.

In addition to normal deterioration, bearings may fail due to heat seizure, fracture, scoring of the rings and other conditions caused by improper use, selection or maintenance of the bearing. Such failures are not normal and can only be avoided by careful handling and correct operation of the bearing in a given application.

BASIC BEARING FATIGUE LIFE

The basic fatigue life of a rotating deep-groove ball bearing is given as:

10⁶

revolutions

L₁₀=

where:	L₁₀	=	rated fatigue life with a statistical reliability of 90%
	P	=	bearing equivalent load
	C	=	basic radial dynamic load rating (see individual bearing selection charts)

TEMPERATURE CORRECTION FACTOR

If rolling bearings are used at high temperature, the hardness of the bearing steel decreases. Consequently the basic radial dynamic load rating C must be corrected:

C_t = f_t • C

Bearing temperature ^oC	< 150	175	200	250
Temperature factor f_t	1.00	0.95	0.9	0.75

Note: The temperature correction factor assumes that a lubricant is used that is suitable for given temperature.

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